The present generally invention relates to the backup of data stored in a cache memory of a storage system.
As a technology on the backup of data stored in a cache memory, a technology disclosed in Japanese Patent Application Laid-Open No. 2002-99390, for example, is known. According to Japanese Patent Application Laid-Open No. 2002-99390, if power from the outside is shut down in a state where data, which has not yet been saved to a disk, exists in a cache memory, the data in the cache memory is copied to a non-volatile memory while a battery can supply power. After copying completes, power from the battery continues to the cache memory. When the power supply from the outside is restarted, the data stored in the cache memory is used if the power supply from the battery continues, or the data is restored from the non-volatile memory to the cache memory if the battery power has run down.
Recently the storage capacities of cache memories are increasing because of the increase in the capacities of memory chips constituting cache memories, and the higher performance of storage systems. Therefore there is concern over the increase of system down times. “System down time” is the time from the storage system stopping acceptance of I/O commands from a host device (e.g. host computer) to restarting the system. If the end of system down time, which was started at a certain point (e.g. time of power shut down, at which power from a primary power supply to the cache memory stopped due to a power failure, for example), is the completion of returning the data from the non-volatile storage resource to the cache memory, the time length required for this returning data (for convenience, returning data from the non-volatile storage resource to the cache memory is called “staging”, and the time length required for the returning data is called “staging time length” in the following description) influences the length of the system down time. Since the storage capacities of cache memories are increasing, as mentioned above, the data volume of staging increases, and staging time length increases accordingly. As a result, the system down time becomes lengthy. Generally a storage system is demanded to be operational 24 hours/365 days non-stop, so as to present no hindrance to the work of the user, therefore a lengthy system time is a problem.